Originally Posted by ak

Depending on the TA, you might be asked to pay 3% (for VISA/MC, more for AMEX) to cover the TA's transaction costs.

Interestingly, when I was recently trying to buy a round trip ticket directly from CX in BKK, they informed me that I would need to pay an additional 3% to use my CC. I was quite surprised since the fare was a published fare.